This research is part of a general program to measure the electronic structure of biologically important molecules in those instances where there is good evidence that the electronic structure is essential to the biological function. The present work is concerned with the visual pigments. In order to understand the process of vision on a microscopic scale it is necessary to determine the nature of the interactions between opsin and retinal, both before and after the absorption of a photon. This description in turn rests on a detailed description of the electronic states of the visual pigments and their behavior under perturbation. This description is to be derived from measurements of the optical absorption, emission, infrared and Raman spectra of model polyenes, the isomers of retinal and their Schiff bases as well as vertebrate rhodopsin. Effort is also being made to prepare complexes of retinal and its derivatives with proteins other than opsin that are more tractable to experimental study. The emphasis is on developing new information by exploiting recent advances in polyene electronic structure, solvent shift theory, and the application of tunable lasers to solve spectroscopic problems. BIBLIOGRAPHIC REFERENCES: B.E.Kohler, "Visual Chromophore Electronic Structure," Biophysics of Structure and Mechanism, 00, 0000 (1977), in press. J.P. Corsetti and B.E. Kohler, "Ground and Excited State Dipole Moments of all-trans Retinal and all-trans Retinylidene-n-butylamine in Solution," J. Chem. Phys., 00, 0000 (1977), in press.